Supercritical Fluid Extraction (SFE) is the process of separating one component (the extractant) from another (the matrix) using supercritical fluids as the extracting solvent. Extraction is usually from a solid matrix, but can also be from liquids. SFE can be used as a sample preparation step for analytical purposes, or on a larger scale to either strip unwanted material from a product (e.g. decaffeination) or collect a desired product (e.g. essential oils). Carbon dioxide (CO2) is the most used supercritical fluid, sometimes modified by co-solvents such as ethanol or methanol. Extraction conditions for supercritical carbon dioxide occur above the critical temperature of 31° C. and critical pressure of 74 bar.
CO2 can act as an effective solvent in both liquid and supercritical phases. CO2 is known as a “tunable solvent” making it versatile for extracting a multitude of end products by controlling temperature, density and phase. These phase changes create an environment to extract differing weights of components from the plant material.
In the CO2 system the solvating power can primarily be regarded as being a function of density and temperature within a static volume, with the solvent density being the more important factor. Heat provides kinetic energy thereby generally increasing solubility of target solutes, while varying CO2 density provides ability to create a dissolution bias based on the solute's molecular attributes, such as symmetry, size and polarity in relation to the number of super critical carbon dioxide (SCCO2) molecules required to dissolve individual solute molecules.
Currently known extraction methods using SCCO2, involve density manipulation independent of temperature via specialized mechanical pumps to achieve extraction bias towards specific compounds. Typically, mechanical pumps are used to force liquid CO2 at high pressure into a static volume to increase CO2 density to the desired level, whereafter the temperature is manipulated to generate the desired SCCO2 condition. As the SCCO2 flows through the plant material, a variety of components (“solute”) can be dissolved in the SCCO2. The extract-laden SCCO2 is then transferred to another vessel where it is depressurized with the subsequent fall in density changing the SCCO2 to gaseous CO2, causing the solute to separate from the gaseous CO2. The gaseous CO2 is then subjected to a heat exchanger where it is cooled to liquid state and then pumped again to repeat the cycle.
For certain plant extracts (such as CBD cannabinoid solubility in CO2 occurs when the density of CO2 is 756 kg/m3—at around 53° C. at ˜2814 psi. At this density, the CO2 is in supercritical phase and there are sufficient intermolecular spaces, and the spaces are of sufficient volume to hold CBD molecules in solution. If the density is higher, the spaces may become too small to accommodate the CBD molecules and if the density is too low, the spaces may be too large to hold the CBD in solution. In either case extraction efficiency is not optimal.
Liquid CO2 is generally commercially available in supply tanks, often at ˜800 psi at ˜21° C., wherein ˜67% of CO2 exists in liquid phase and ˜33% in gas phase. In this state the CO2 tank is considered full, and combined density may be ˜550 kg/m3. If such a supply tank is connected to a constant volume extraction vessel, the pressures would equalize with the extraction vessel containing liquid and gas with a combined density of ˜550 kg/m3. This level of density may be insufficient for efficient encapsulation of the desired solute molecules and attempted extractions using this density will result in little or no extract. Therefore, mechanical pumps are used to physically force CO2 into the extraction vessel until the desired density is reached.
U.S. Pat. No. 8,895,078, discloses a method for producing an extract from cannabis plant matter, containing tetrahydrocannabinol, cannabidiol and optionally the carboxylic acids thereof, wherein specific temperature/pressure combinations are presented for the various cannabinoids along with the use of mechanical pumps. In the method of this patent, pure CO2 is conveyed via a conduit to a liquefier equipped with a condenser coil, and then liquid CO2 is supplied via a pressurizing pump to a heat exchanger, to be available for the extraction cycle described therein.
In the Sandia National Laboratories 2010 report “Operation and Analysis of a Supercritical Braydon Cycle” (http://prod.sandia.gov/techlib/access-control.cgi/2010/100171.pdf), the descriptions and associated drawings clearly show mechanical pumps being used to control the density.
In extraction processes involving mechanical pumps, as the SCCO2 is forced through the raw material at high rates, the SCCO2 does not become fully impregnated, much less saturated with solute, and is subject to “channeling” whereby the SCCO2 flow finds the path of least resistance, thereby bypassing some of the potential extracts. Different manufacturers have different flow rates and different ways of dealing with efficiency but they all function substantially in the same manner. Moreover, recycling of recovered CO2 in these extraction processes can carry solute over into the pump causing the pump to malfunction and require service. Furthermore, mechanical pumps are expensive, noisy, and require high maintenance and often special infrastructure.
Hydrocarbon co-solvents have also been used in extraction processes involving SCCO2. The hydrocarbon-enhanced extraction processes, however can leave residues in the extracts.
Accordingly, there is need for alternative cost effective and environmentally friendly extraction methods.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.